The invention relates in general to a displaying devices More particularly, the present invention provides a method and system capable of repairing the electrical defects in a displaying device using a predetermined pattern. Merely by way of example, the invention has been applied to liquid crystal displays, commonly called LCD, although there could be other applications.
With certain advantages of size, weight, low power consumption and no radiation contamination, liquid crystal displays (“LCD”) have been widely used in recent years. The resolution of the LCD is determined according to the number of pixels. The LCD with a larger number of pixels presents a more delicate and detailed displayed image. Details of conventional LCDs are provided below.
A conventional tin film transistor liquid crystal display (TFT-LCD) has a first plate and a second plate. The first plate comprises a number of transparent pixel electrodes, color filters, and black matrices. The second plate comprises a number of scan lines, data lines, storage capacitors, switching elements (e.g., TFTs), and transparent pixel electrodes. In a TFT-LCD, the data lines perpendicularly intersect the scan lines to form a number of pixel regions. Thus, each pixel region is defined by a pair of scan lines and the corresponding data lines. Each pixel region includes a storage capacitor CST, a TFT, and a pixel electrode (e.g. a transparent ITO). The space between the first plate and the second plate is filled with numerous LC molecules. The polarizing films are generally disposed on the outer surfaces of the first plate and the second plate. A direct-view transmission type TFT-LCD further includes a backlight module for providing a light source of LCD.
FIG. 1A is a cross-sectional view taken along the line 1A-1A of FIG. 1C illustrating a conventional thin film transistor (TFT) of a second plate of LCD. A conventional method for manufacturing a TFT is described below. First, a substrate 102 is provided and a first metal layer is formed on the substrate 102. The first metal layer is then patterned to form a gate electrode 104. Next, a first insulating layer 106 is formed on the substrate 102 and covers the gate electrode 104. An amorphous-Si (a-Si) layer is formed on the first insulating layer 106 and then patterned to form a channel 105. After that, a second metal layer is formed on the insulating layer 106 and covers the channel 105. By performing a photolithography process, the second metal layer is patterned to form a drain D and a source S. Next, a passivation layer 108 is formed on the drain D and the source S and covers the first insulating layer 106. A via 110 is then formed within the passivation layer 108 to expose the partial surface of the source S. Finally, a pixel electrode (e.g. transparent indium tin oxide (ITO)) 112 is formed on the passivation layer 108 and fills the via hole 110 so that the pixel electrode 112 is electrically coupled to the source S.
The scan lines and data lines are respectively formed during the patterning step of forming the gate and the source/drain (S/D). Also, the scan lines and data lines are isolated by the first insulating layer 106.
FIG. 1B is a simplified cross-sectional view taken along the line 1B-1B of FIG. 1C illustrating a storage capacitor (CST) of a second plate of LCD. A conventional method for manufacturing a storage capacitor is described below. A storage capacitor (CST) is formed with a common electrode 114 and a capacitor electrode 116. As shown in FIG. 1B, the common electrode 114 and the capacitor electrode 116 are separated by the first insulating layer 106. The storage capacitor (CST) is formed together with the formation of the TFT. The common electrode 114 is formed after the formation and patterning of the first metal layer. Likewise, after the formation and patterning of the second metal layer, the capacitor electrode 116 is formed. The passivation layer 108 covers the capacitor electrode 116 and the first insulating layer 106. A via hole 118 is formed within the passivation layer 108. When the pixel electrode 112 is formed over the passivation layer 108, the pixel electrode 112 and the capacitor electrode 116 are electrically coupled through the via hole 118. In addition, storage capacitors of the pixels of the TFT-LCD have their common electrodes connected to a common voltage of the TFT-LCD. The storage capacitors of the pixels are used for controlling the voltage applied to the LC molecules. The common electrodes 114 of the storage capacitors can be connected to the adjacent scan lines. However, for reducing the drawback of gate delay during LCD driving, a “CST on common” (i.e. storage capacitors on a common electrode) becomes the general trend in TFT-LCD design.
In addition, a transparent electrode is further formed on a glass substrate of the first plate of the conventional TFT-LCD. The first plate is assembled with the second plate, and the space therebetween is filled with numerous LC molecules. The polarization of the light passing through the liquid crystal layer is modulated by changing the alignment of the liquid crystal molecules that is varying with a voltage applied to the pixel electrode. According to the alignment of LC molecules and driving method, the TFT-LCD can be categorized into several modes, including vertical alignment mode (e.g. patterned vertical alignment (PVA) and multi-domain vertical alignment (MVA)), twisted nematic (TN) mode and in-plane switch mode. Many researches have reported that the visual effect of VA mode TFT-LCD can be improved by arranging the orientation of the LC molecules within a pixel into different groups. For example, a MVA mode TFT-LCD comprises a regional adjusting structure (e.g. a slit of a pixel electrode) for arranging the orientation of the LC molecules. When a voltage is applied, the LC molecules within a pixel are inclined to different directions so as to form the multi domains for improving the visual effect. In addition, after a voltage is applied, a capacitor of liquid crystal (CLC) between the pixel electrode 112 of the second plate and the transparent electrode of the first plate is generated, and the value of CLC depends on the effective area of the pixel electrode 112.
FIG. 1C schematically illustrates a single pixel of a multi-domain vertical alignment (MVA) mode TFT-LCD. As shown in FIG. 1C, each pixel controlled by the data line (DL) and the scan line (SL) comprises a thin film transistor (TFT) 107, a pixel electrode (PE), and a common electrode (VCOM) of the storage capacitor. The common electrode (VCOM) of FIG. 1C is the patterned first metal layer (denoted as 114) of FIG. 1B. The capacitor electrode 116, the patterned second metal layer, is formed above the common electrode 114, and the pixel electrode 112 on the top is electrically connected to the capacitor electrode 116 through the via hole 118. Also, the slit 120 on the pixel electrode 112 is formed for the purpose of the effect of wide viewing angle. Furthermore, a protrusion formed on the first plate is used as the regional adjusting structure 111. In the PVA mode TFT-LCD, a slit of the transparent electrode of the first plate is used as the regional adjusting structure 111.
Over the years, LCD displays have proliferated from computer screens, mobile devices, and large flat panel displays used for television sets. Unfortunately, certain limitations still exist. As merely an example, certain pixels of the LCD could be electrically damaged due to manufacturing. Those damaged pixels, not being normally controlled by the electrical signals, degrade the displaying quality of the LCD. Such defects may occur during the manufacture of the second plate of TFT-LCD. For example, the incorrect pattern of electrodes formed by a bad photolithography process or the particle contamination occur on the second plate can cause the short circuit between the pixel and the data line. The pixel having the electrical defect (e.g. short-circuit) is a display flaw in the TFT-LCD.
FIG. 1D schematically illustrates a conventional method of repairing the defect on the pixel of FIG. 1C. As shown in FIG. 1D, a defect D1 occurs at the position which causes the electrical connection between one of the common electrode 114 and the data line (DL) and one of the capacitor electrode 116 and pixel electrode 112. The voltage applied to the common electrode or the signal originally transmitted through the DL into the pixel electrode is send into the pixel through the defect D1. Thus, the signal transmission to this pixel cannot be controlled by the TFT 107. FIG. 1E is a cross-sectional view taken along the line lE-lE of FIG. 1C illustrating a defect occurring between the data line and the capacitor electrode. As shown in FIG. 1E, the data line and the second metal layer (i.e. capacitor electrode) 116 are at the same level, and it is easy to be short circuit if a defect such as a particle occurs on the position depicted in a dashed-circle. Since the defect is positioned above the common electrode 114, laser cutting for removing the defect will also damage or cut the common electrode 114 off so that the reference voltage won't be successfully transmitted to the pixels in the same rows through the common electrode. Accordingly, a conventional method for repairing the defect was developed by removing the pixel electrode at the periphery of the common electrode (e.g. laser cutting along the cutting lines C1, C1′) for eliminating the interference (i.e. short circuit) caused by the defect D1.
The conventional method has a serious drawback of giving up the whole capacitor electrode 116 and over half a pixel electrode (i.e. the area above the cutting line C1 being unworkable). The overall capacity of each pixel, equal to the storage capacitor (CST) and the capacitor of liquid crystal (CLC) before repairing (i.e. CTOTAL=CST+CLC), is decreased to less than half a capacitor of liquid crystal after repairing (i.e. CTOTAL<(½)×CLC). Accordingly, the workable pixel electrode area (less than half a pixel electrode) greatly decreases the effective displaying region of a pixel. Moreover, the voltage required for driving LC cannot be steadily maintained in a displaying period due to an absence of the storage capacitor of capacitor electrode, so as to decrease the displaying quality of the pixel.
In addition, if the defect (such as a particle) occurring at the position near the via hole 118 results in the short circuit between the pixel electrode 112 and the capacitor electrode 116, the voltage required for driving LC also cannot be steadily maintained in a displaying period so as to decrease the displaying quality of the pixel.
Similarly, the conventional repairing method applied to other conventional types of TFT-LCD has the issue of decrease of displaying quality.
FIG. 2A schematically illustrates a single pixel of a CST-On-Gate TFT-LCD. FIG. 2B schematically illustrates a conventional method of repairing the defect on the pixel of FIG. 2A. In a CST-On-Gate TFT-LCD, the capacitor electrode 116 is positioned on the gate line (GL), and the pixel electrode 112 is electrically connected to the capacitor electrode 116 through the via hole 118. When a defect D2 occurs to cause a short circuit between the DL2 and the capacitor electrode 116, a portion of the pixel electrode 112 corresponding to the capacitor electrode 116 is removed; for example, by laser cutting along the cutting line C2. However, the whole storage capacitor and part of the capacitor of liquid crystal have been given away.
FIG. 3A schematically illustrates a single pixel of an in-plane switch (IPS) mode TFT-LCD. FIG. 3B schematically illustrates a conventional method of repairing the defect on the pixel of FIG. 3A. The pixel electrode 312 and the field electrode 317 are oppositely arranged as two staggered forks. Also, the field electrode 317 is electrically connected to the capacitor electrode 116 through the via hole 118. The LC molecules of IPS mode TFT-LCD are driven by the electrical field between the pixel electrode 312 and the field electrode 317, and the displaying result depends on whether the backlight source penetrates the LC molecules or not. Since the capacitor electrode 116 and the data line DL are almost at the same plane, a defect D3 occurs at the dashed-circle position can easily cause a short circuit between the capacitor electrode 116 and the data line DL. The conventional repairing method is to remove parts of the field electrode 317 around the via hole 118, for example, by laser cutting along the cutting lines C3, C3′. The IPS mode TFT-LCD is normally black in an absent of electrical field. After applying the conventional method, this uncontrollable pixel is always presented as a dark point of TFT-LCD. Although no bright point of TFT-LCD is observed, the issue of electrical defect has not been solved at all.
According to the conventional repairing method described above, no matter what types of TFT-LCDs have to give up the whole storage capacitor. Even more than half a capacitor of liquid crystal has to be given up. The voltage required for driving LC cannot be steadily maintained in a displaying period (e.g. 16.67 ms at a display frequency of 60 Hz) by insufficient storage capacitor, so as to decrease the displaying quality. Also, cutting a large portion of pixel electrode greatly reduces the effective displaying region of a pixel. Therefore, how to decrease the effect of short circuit between electrodes, and effectively repair the electrical defect without degrading the display quality is an important goal to be achieved.
From the above, it is seen that improved techniques for manufacturing LCDs are highly desired.